1. Field of the Invention
The present invention relates to an endoscope apparatus for obtaining an image by means of an image pickup element for picking up images of an object by integrating charges.
2. Description of the Related Art
Conventionally, an endoscope apparatus includes an endoscope such as an electronic endoscope having a solid image pickup element, a processor, a light source apparatus and a monitor in general. In the conventional endoscope apparatus, an insert portion of the endoscope is inserted into a body cavity. Here, light is irradiated from the light source apparatus to an object through a light guide contained in the endoscope and is reflected from the object. The solid image pickup element provided at the distal end of the endoscope optoelectronically converts the reflected light. Then, the processor signal-processes the output signals resulting from the optoelectronic conversion, and the signals are displayed on the monitor.
Recently, a technology has been used for irradiating an exciting light to a part to be observed of a living-body tissue, imaging auto fluorescence occurring from the living-body tissue from the exciting light or photodynamic diagnosis (PDD) using fluorescence drugs called photosensitizers as a two-dimensional image, and diagnosing a lesion (such as a type of disease and an invasive range) of a cancer, for example, based on the fluorescent image. Florescent observation apparatuses for performing fluorescent observation have been developed.
Regarding auto fluorescence, when exciting light is irradiated to a living-body tissue, fluorescence is generated by the exciting light at the longer wavelength side than that of the exciting light. A fluorescent material in a living body may be nicotin amide adenine dinucleotides (NADH), Flavin mono nucleotide (FMN) or collagen and the like. Recently, the correlation between a biological endogenous compound generating such fluorescence and a disease is being clarified, and a cancer, for example, can be diagnosed by observing the fluorescence.
Regarding PDD, HpD(hematoporphyrin), Photofrin or ALA(δ-amino levulinicacid) and the like may be used as a fluorescent material to be injected into a living body. These photosensitizers can be uniquely accumulated onto a cancer, for example, and a lesion can be diagnosed by injecting these photosensitizers into a body and observing fluorescence. Alternatively, a fluorescent material may be added to monoclonal antibiotics, so that a fluorescent material can be accumulated in a lesion through an antigen-antibody reaction.
For example, the fluorescence observing apparatus may adjust and control the sensitivity of a CCD type solid image pickup element provided at the distal end of an endoscope so as to achieve a constant screen average of fluorescent images, that is, to achieve a constant intensity average of a monitor.
In order to image weak fluorescence by using the fluorescence observing apparatus, an aperture in the light source is fully opened, and the sensitivity of a charge-multiplying solid image pickup element having adjustable sensitivity is multiplied. Then, the sensitivity of the charge-multiplying solid image pickup element is further automatically gain-controlled so that a fluorescent image can be obtained.